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In Reply to: Question regarding Futterman vs Atma-Sphere posted by SamWalters on July 25, 2006 at 15:12:29:
Atma-sphere amps use a circlotron output stage, not the totem pole type of output stage found in Futterman amplifiers and patented by Julius Futterman. Go look up these topologies in an electronics book and you will see how different they are. There is some information on Kevin Covi's website, for example. That's for starters. In addition, Atma-sphere amps are fully balanced from input to output, whereas Futterman amplifiers are single-ended. Atma-sphere amps, being all-triode and mostly class A operation are quite happy with no applied negative feedback (NFB), whereas the Futterman circuit requires heaps of NFB to maintain stable operation. Atma-sphere amps are direct-coupled at the output, whereas the standard Futterman design mandates large electrolytic coupling capacitors at the output. (A few renegade Futterman-type amplifiers are direct-coupled, and most of those are dangerous to speakers.) There's more. To sum it up, the only thing these two types have in common is that they are both said to be "OTL", but remember that Futterman amps need those coupling capacitors in lieu of an output transformer. Having said all of that, I do not wish to be seen as putting down Futterman amplifiers. I owned at least six different pairs of Futterman-type monoblocks over a 25-year period, and I was happy until I discovered Atma-sphere. IMO, the Atma-sphere design sounds better, period. If you should decide in favor of a Futterman-type amplifier, then I would recommend that you consider Transcendent. Some of the inherent problems associated with the Futterman circuit have been solved by Transcendent's designer, Bruce Rozenblitt. And why would you expect to pay $10,000 for a used Atma-sphere amplifier? (Lets assume you can find one on eBay or Audiogon; the price will be way less than that.) Why is the Futterman amplfier only $750? Well, Julius died in 1979, so if it's a true Futterman amp, it's at least 27 years old. may need new caps, etc. I don't think you've done any homework on this and that you just want to be provocative.Oh yeah, you asked what is the "benefit" of either type of amplifier. Answer: good sound. No output transformer. Neither of them pay royalties, as far as I know.
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Follow Ups
- Most of your assumptions are incorrect - Lew 07:32:52 07/26/06 (0)
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